Background : Fetus in fetu (FIF) is a rare congenital anomaly and is defined as monozygotic twin incorporated into the abdomen of its sibling during development the incidence is 1 per 500,000 births.
Case Presentation Summary : A 7 month old boy with a large non tender mass of variable consistency on the left lumbar region. Abdominal CT-Scan revealed long bone (Figure 1). The patient was then diagnosed with FIF. Elective laparotomy was performed and a large retroperitoneal cystic mass in the shape of fetus (19x16x11 cm, 550 gram) was found attached to the lower pole of the left kidney.The fetus was anencephalic with malformed trunk, buttocks, intestine, and two lower limbs (figure 2).
Learning Points/Discussion : Fetus in fetu is the malformed or parasitic monozygotic diamniotic twin found inside the body of a living child. Fetus in fetu was mostly found in the upper retroperitoneum, while teratoma usually appears in the lower abdomen, ovaries, or sacrococcygeal region. In our case the mass was in the retroperitoneum.The vertebral column and the limbs present in the fetus in fetu in almost all cases [91% and 82.5%, respectively]. Imaging modalitiesallow us to accurately diagnose the condition before surgery. Surgical excision is the recommended treatment.

Keywords: fetus in fetu teratoma Imaging modalities

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